Loss of chromosome 7 (monosomy 7) and deletion of a segment of the long arm [del(7q)] are recurring eytogenetic abnormalities that are detected commonly in de novo and therapy-induced myeloid malignancies, and are associated with a poor prognosis. In work supported by this P01 award, cytogenetic analysis delineated two commonly-deleted segment (CDSs) in patients with myeloid disorders characterized by a del(7q): one located in band q22 that accounts for most cases and another in bands q32-34. Using an ordered set of yeast artificial chromcsome (YAC) clones as probes, fluorescence in situ hybridization (FISH) experiments were then performed on leukemias with deletion breakpoints within 7q22. These studies implicated a -2.5 Mb CDS as harboring a TSG that is inactivated in these myeloid malignancies. During the initial period of support for this Project, we analyzed leukemia samples for allele loss and for homozygous deletions within the CDS. We also ordered a series of overlapping bacterial artificial chromosome (BAC) clones to produce a contig spanning >95% &this interval. Genomic sequences from these BACs were instrumental for identifying 19 known and novel genes/cDNAs that we have cloned. To date, we have fully evaluated 8 of these as candidate TSGs. A number of unique expressed sequence tag (EST) clones, Unigene clusters, and THC consensus alignments have also been mapped within the region can be used to clone additional candidate TSGs. Our underlying hypothesis is that a novel myeloid TSG resides within this 7q22 CDS is inactivated in myeloid malignancies characterized by monosomy 7 or by a del(7q). We will take advantage of extensive data generated during the initial period of support and of the large and diverse collection of leukemia samples available to us to pursue this hypothesis through four aims: (1) to complete and annotate a contig comprised of fully sequenced clones spanning the entire 7q22 CDS, (2) to use microarray technology to analyze gene expression across the CDS, and to use this data to select prioritize candidate TSGs for cloning and mutation analysis, (3) if mutations of a gene located in 7q22 are identified to ascertain the spectrum of mutations in leukemia and to characterize its function in myeloid growth control in tissue culture and mouse models, and (4) to use embryonic stem cells engineered to model loss of the 7q22 CDS to test the idea that haploinsuffiency for a TSG within this interval perturbs myeloid growth.